1. Field of the Invention
This invention relates sprocket chain dampers and particularly to bicycle sprocket chain dampers.
2. Description of Related Art
Bicycles have developed over the past 20 years into much more than a simple means of transportation. High performance, multi-gear bicycles have been developed for racing, road touring and for off-road uses. The off-road bicycles are typically called "mountain bikes". These high-performance bikes create high-performance problems. One such problem is called "chain suck". This occurs when riding a bicycle over rough terrain. At these times, there are intervals during which the drive chain, particularly along its lower (return) run is subjected to varying high forces and vibration. During these intervals, the chain can whip wildly. Often, if the drive sprocket is cranked while the chain is whipping, the loose chain becomes jammed, or wedged, between the sprocket and the bicycle frame. This jamming is called "chain suck". Poor or missed shifting can be also caused by chain whip.
Several attempts have been made to avoid this problem. U.S. Pat. No. 5,397,275 teaches a solid damper that is nothing more than a split tube that is placed over the lower portion of the chain, with one end attached to the idler pulley support. The tube is designed to allow the free movement of the chain through it, under normal conditions, but its rigid body prevents wild whipping during fast, bumpy riding. Despite the advantages of this device, in practice, it does not offer a sound solution. The tube can become filled with dirt or other materials that prevent the smooth operation of the chain through it. If the tube is too rigid, it may work to over damp the chain. Such constrictions can cause problems in smooth pedaling or shifting of gears, as well as noise.
U.S. Pat. Nos. 4,786,071 and 4,960,402 teach devices to help control the chain movement. These devices, however, do little to prevent the whipping action that causes chain suck. Rather, these devices attempt to prevent the chain from becoming stuck only after the chain already has been displaced, e.g., by the forces encountered when cycling downhill off-road at high speeds.